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The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD – a monozygotic twin study

Timothy Hall1, Cherrie Galletly127*, C Richard Clark3, Melinda Veltmeyer48, Linda J Metzger, Mark W Gilbertson4, Scott P Orr5, Roger K Pitman5 and Alexander McFarlane6

Author Affiliations

1 Discipline of Psychiatry, School of Medicine, University of Adelaide, Adelaide, Australia

2 Ramsay Health Care (SA) Mental Health Services, Adelaide, South Australia

3 Cognitive Neuroscience Laboratory and School of Psychology, Flinders University of South Australia, Adelaide, Australia

4 Veterans Affairs Medical Centre Research Service, Manchester, New Hampshire, England

5 Massachusetts General Hospital and Harvard Medical School, Boston, USA

6 The Centre of Military and Veterans’ Health, Adelaide, Australia

7 Northern Mental Health, Adelaide Metro Mental Health Directorate, Adelaide, South Australia

8 Harvard Medical School, Boston, USA

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Biology of Mood & Anxiety Disorders 2012, 2:21  doi:10.1186/2045-5380-2-21

Published: 1 December 2012



PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD.


Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins.


There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD.


These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.